Pyrometers come in two forms:
1) A device for measuring the temperature of a molten pool, comprising: a refractory mounting sleeve and an optical pyrometer;
2) Generally refers to the thermometer used to measure the temperature higher than 500℃. Commonly used pyrometers include optical pyrometers, colorimetric pyrometers and radiation pyrometers.

In addition, thermocouple thermometers can also be used to measure high temperatures below 3000°C. But because the measuring range of thermocouple thermometer can be as low as -200 ℃, it is generally not classified as a pyrometer.
The temperature indication on the optical pyrometer can be determined using a standard temperature lamp. The standard temperature lamp is shown in Figure 1b, it can reproduce the brightness temperature in the range of 900~2500℃, and can also be used as a light source
The temperature of 700～3000℃ can be measured by using the hidden wire optical pyrometer. Higher temperatures can also be measured by replacing the bulb and the attached absorbing glass for the objective.
The measurement range of the colorimetric pyrometer is 800 to 2 000 °C, and the measurement accuracy can be close to ±1% of the upper limit of the range. The advantage of a colorimetric pyrometer is that the measured color temperature values are very close to the true temperature.